In a report published earlier this year,, external the UK’s independent adviser on tackling climate change, the Climate Change Committee (CCC), estimated that 92% of existing homes would be at risk of overheating by 2050.
Speaking to Matt Chorley on Radio 5 Live, Farron said: “We want to make sure that we’re not being hysterical but we’re recognising that we have more extreme temperatures, more extreme weather.
“I want the homes that people live in in the future to be ready for that, that we be climate-ready and prepared.”
The party said the cost of its policy to developers would be small compared to the overall cost of building a home, and that cooler homes would be more attractive to buyers in the future.
Farron said forms of air cooling systems should be installed without adding “to the climate crisis”, pointing to the potential of air source heat pumps.
There have been concerns that while decreasing temperatures indoors, air conditioning units can increase outdoor temperatures.
Michael Whittall, sustainability manager at property developer Fairview New Homes, told news agency PA: “Air conditioning systems work by removing heat from inside buildings and releasing it outdoors.
“When this happens at scale, particularly in dense urban areas, it can contribute to the urban heat island effect – adding to higher outdoor temperatures and increasing heat stress in cities.”
He said the focus should be on “passive cooling” such as better designs, shading and ventilation.
Amanda Williams, head of environmental sustainability at the Chartered Institute of Building (CIOB), said air conditioning or reversible heat pumps would “undoubtedly have a crucial role in some circumstances”.
However, she added that making it the default option “risks locking in higher energy consumption” and that the priority should be designing homes that “remain comfortable for as much of the year as possible”.
A spokesperson for the Home Builders Federation said: “New build homes are required to be exceptionally well insulated which helps keep them both warmer in winter and cooler in summer.
“This makes living in a new build more comfortable and significantly cheaper to run than older, less well-insulated homes.”
The Liberal Democrats have also argued that the government should fund the cost of fitting essential buildings such as schools and hospitals with air conditioning.
The party said the costs of inaction dwarfed the costs of acting immediately, pointing to the CCC’s report, external which said climate impacts could cost £60bn – £260bn a year compared to the £7bn – £22bn it would cost to protect people from the impacts.
The Lib Dems said the cost of fitting hospitals with air conditioning would come from its £10bn investment plan for the NHS.